The present invention relates generally to dipeptide compounds and, more particularly, to novel dipeptide analogs and compositions, their preparation and their use as modulators of the immune system.
New therapeutic and diagnostic agents have begun to emerge from discovery efforts which use high-throughput screening directed to certain gene-specific transcription factors.
One family of transcription factors responsible for transmitting a signal to a cell""s nucleus are the proteins known as Signal Transducers and Activators of Transcription (STATs; see: Damell et al. (1994) Science 264: 1415; for review, see: e.g., Ihle et al. (1994) Trends Biochem. Sci. 19:222; Mile et al. (1995) Trends Genetics 11:69); and Horvath et al. (1997) Curr Opn Cell Biol, 9:233). STATs are activated by contact with the phosphorylated cytokine receptor, activation results in the STAT polypeptides forming a dimer and entering the nucleus, where the STAT dimer binds to the regulatory region of a gene that is inducible by the particular cytokine. Binding of the activated STAT dimer triggers transcription of the gene.
The STAT polypeptides (STAT1, STAT2, STAT4, STAT5a, STAT5b, and STAT6) have molecular masses from 84-113 kDa Each STAT protein contains a Src homology-2 (SH2) domain capable of recognizing one or more phosphotyrosine sequences in the cytoplasmic portion of the activated receptor (Shuai et al. (1993) Nature 366: 580). Additionally, each cytokine receptor is specific for a particular STAT protein, and each STAT activates transcription of certain genes, thereby providing two layers of specificity in cytokine-induced signaling.
STAT6 and STAT4 are two proteins that are intimately involved in regulation of immune responses. STAT4 transduces to the nucleus signals from the IL-12 receptor. IL-12 is involved in the development of a TH1 immune response (Kaplan et al. (1996) Nature 382: 174-177), which is part of an organism""s defense against intracellular pathogens. IL-12 is also necessary for the T-cell-independent induction of the cytokine interferon (IFN)-xcex3, which is a key step in the initial suppression of bacterial and parasitic infections. Knockout mice which lack STAT4 were found to be defective in all IL-12 functions tested, including the induction of IFN-gamma, mitogenesis, enhancement of natural killer cytolytic function and TH1 differentiation (Thierfelder et al. (1996) Nature 382: 171-174).
IL-4 signals are transduced to the nucleus by STAT6. IL-4 is a key cytokine in the initiation of a TH2 immune response, and also activates B and T lymphocytes. STAT6-deficient mice were shown to be deficient in IL-4 activities (Kaplan et al. (1996) Immunity 4: 313-319; Takeda et al. (1996) Nature 380: 627-630; Shimoda et al. (1996) Nature 380: 630-633).
Because of the importance of STAT4 and STAT6 in modulating the immune response of an organism, both in response to infection and in undesirable conditions such as inflammation, allergic reactions, and autoimmune diseases, a need exists by which the clinician can diagnose, enhance or reduce STAT4 and STAT6 signals. Intervention at the STAT level would have significant advantages compared to previous approaches, which typically target the IL-4 or IL-12 cytokine itself, or the interaction of the cytokine with the receptor. Disruption of cytokine function itself can cause a variety of undesirable side effects. These can be avoided by intervening at the level of STAT-mediated signal transduction. However, identification of agents that can modulate STAT4 and STAT6-mediated signal transduction has heretofore been hampered by the lack of suitable assays. Recently, a new assay for identification of STAT6 and STAT4 signaling modulators was described (see, U.S. Pat. No. 6,207,391). Assay of binding of STAT4 and STAT6 to their corresponding receptors, and identification of agents which increase or decrease the degree of such binding, has now led to the identification of compounds which are useful in the diagnosis and treatment of various STAT-dependent conditions.
In one aspect, the present invention provides compounds which are represented by the formula: 
In the above formula, R1 and R2 and are each independently selected from hydrogen, (C1-C8)alkyl, aryl, aryl(C1-C8)alkyl, (C1-C8)heteroalkyl and aryl(C1-C8)heteroalkyl, with the proviso that at least one of R1 and R2 is selected from aryl, aryl(C1-C8)alkyl and aryl(C1-C8)heteroalkyl.
The symbol A1 represents an L-xcex1-amino acid, D-xcex1-amino acid or a radical having the formula: 
in which R3 is hydrogen or (C1-C8) alkyl, and R4 and R5 are each independently selected from hydrogen, (C1-C8)alkyl and (C1-C8)heteroalkyl, or R4 and R5 can be individually combined with F3 to form a 5-, 6-, 7- or 8-membered ring containing from one to three heteroatoms.
The symbol A2 represents an L-xcex1-amino acid, D-xcex1-amino acid or a radical having the formula: 
In the indicated formula, R6 is either hydrogen or (C1-C4)alkyl; R7 and R8 are independently selected from hydrogen, (C1-C8)alkyl and (C1-C8)heteroalkyl, or R7 and R8 can be combined with each other to form a 5-, 6, 7- or 8-membered ring containing from zero to three heteroatoms.
The letter X represents a bond, a (C1-C4) saturated or unsaturated alkyl linking group or a (C1-C4) saturated or unsaturated heteroalkyl linking group. Ar represents an aryl group.
The letter Y represents an acidic moiety, an isostere of an acidic moiety or an ester of an acidic moiety that can be converted to an acidic moiety in vivo. The acidic moiety (or ester or isostere) is attached to Ar either directly or with a spacer. Accordingly, Y can be represented as a radical of formula:
xe2x80x94B1xe2x80x94Z1 or xe2x80x94B2xe2x80x94(Z1)(Z2)
wherein B1 is a bond or a divalent linking group and B2 is a trivalent linking group. The remaining groups, Z1 and Z2 are as follows:
Z1 represents a member selected from xe2x80x94CO2R9, xe2x80x94P(O)(OR9)(OR10), xe2x80x94P(O)(R9)(OR10), xe2x80x94S(O)2(OR9), xe2x80x94S(O)(OR9) and a carboxylic acid isostere. Similarly, the symbol Z2 represents a member selected from xe2x80x94CO2R9, xe2x80x94NHR11, xe2x80x94P(O)(OR9)(OR10), xe2x80x94P(O)(R9)(OR10), xe2x80x94S(O)2(OR9), xe2x80x94S(O)(OR9) and a carboxylic acid isostere. For the listed Z1 and Z2 groups, R9 and R10 each independently represent H, (C1-C8)alkyl or (C1-C8)heteroalkyl; and R11 represents (C1-C8)alkyl.
The compounds of the present invention are useful in compositions that further comprise a pharmaceutically acceptable excipient Both the compounds and compositions of the present inventions are useful for the diagnosis and treatment (including prophylactic treatment) of conditions mediated through STAT signaling. Examples of conditions associated with STAT signaling include, but are not limited to: Th1-mediated conditions such as delayed-type hypersensitivity, contact dermatitis, uveitis, Crohn""s disease, psoriasis and autoimmune diseases (typically associated with STAT4 signaling);
Th2-mediated diseases such as allergic rhinitis, asthma, scleroderma, eczema and conjunctivitis (typically associated with STAT6 signaling); proliferative disorders such as cancers (associated with STAT3 and/or STAT5 signaling); and STAT1 conditions which are similar to those described for STAT4, but typically observed in more acute situations such as acute-transplant rejections. A variety of additional conditions associated with STAT signaling include atopic dermatitis, anaphylaxis, food or drug induced allergy, hypersensitivity reactions, alveolitis, Churg-Strauss syndrome, urticaria, angiodema, and systemic lupus erythematosus.
Other objects, features and advantages of the present invention will be apparent to one of skill in the art from the following detailed description and the claims.